The invention relates to improvements in methods of and in apparatus for monitoring objects in streams of partially overlapping objects, also called scalloped or imbricated streams. More particularly, the invention relates to improvements in methods of and in apparatus for counting sheets, signatures, brochures, pamphlets, newspapers, newspaper sections and like flat objects in a continuous or interrupted stream of partially overlapping objects.
It is known to monitor flat objects (hereinafter called sheets for short) of a stream of partially overlapping sheets by directing a laser beam or a beam of infrared light against successive sheets of the stream and by evaluating the characteristics of the reflected beam. A drawback of such method and apparatus is that the reflectivity of conveyed sheets is likely to vary within a wide range, for example, because the quantity of printed matter varies from sheet to sheet or from a first group of successive sheets to the next group of successive sheets. Moreover, radiation from sources other than a laser or a source of infrared light is likely to distort the signals which are generated by reflected light. Still further, dust including finely comminuted fragments of paper sheets is also likely to affect the accuracy of the counting operation, the same as projecting portions of sheets which move across the path of propagation of a laser beam or a beam of infrared light.